It is well known to the art and literature that a chlorinated vinyl polymer referred to as chlorinated polyvinyl chloride, hereinafter CPVC, has excellent high temperature performance characteristics, among other desirable physical properties. Typically, commercial CPVC has about 57 percent to about 69 percent by weight of bound chlorine, and is most conveniently prepared by the chlorination of polyvinyl chloride (hereinafter PVC) as described in U.S. Pat. Nos. 2,996,489; 3,100,762; 3,334,077; 3,334,078; 3,506,637; 3,534,013; 3,591,571; 4,049,517. U.S. Pat. No. 5,216,088 describes a two step process for forming CPVC containing at least 70 percent by weight chlorine.
The term CPVC is used herein to define a chlorinated vinyl chloride polymer having in excess of about 57 percent by weight of bound chlorine based upon the total weight the polymer. CPVC has become an important specialty polymer due to its relatively low cost, high glass transition temperature, high heat distortion temperature, outstanding flame and smoke properties, chemical inertness, and low sensitivity to hydrocarbon feed stock costs. The glass transition temperature of CPVC generally increases as the percentage of chlorine increases. However, as the chlorine content increases, the CPVC resin becomes more difficult to process. In addition, a well known undesirable characteristic of CPVC resin is that it inherently has low impact properties, a characteristic which is also common to vinyl chloride homopolymers.
The poor processability of CPVC resins is exemplified by milling CPVC on a two roll mill at elevated temperatures which results in high torque and high temperatures as well as decomposition of the CPVC. Softening additives or plasticizers have been added to CPVC in order to improve its processability. Although its processability is somewhat improved, these additives produce undesirable effects. Some of the more significant detrimental effects produced by inclusion of these softening or plasticizer additives are lower heat distortion temperatures, softness and weakness in terms of lower tensile strength, and less desirable chemical properties than those exhibited by CPVC alone. These negative attributes of the additives on CPVC impede the usefulness of the modified CPVC in the manufacture of rigid plastic articles.
The increasing demand for CPVC pipes, vessels, valve bodies and fittings, and the fact that an impact-deficient CPVC matrix can be improved by compounding and blending it with other polymers, has instigated concerted efforts to develop better impact modified compounds. Most of these efforts have been channeled toward rigid CPVC applications where acceptable impact strength and dimensional stability under heat are critical. These include the manufacture of exterior structural products, rigid panels, pipes and conduits, injection-molded and thermoformed industrial parts, appliance housings, and various other types of containers, both large and small.
U.S. Pat. No. 3,264,375 to Robert W. Jones relates to rubber-modified styrene-type polymers. More particularly, the Jones Patent relates to processes for preparing such materials and for producing rubber-in-monomer solutions to be employed in preparing such materials.
U.S. Pat. No. 4,173,598 to Castelazo et. al. relates to processes for making polymeric compositions which have methacrylic and/or acrylic chains grafted onto a copolymerized vinyl diene substrate. The compositions are particularly useful as impact modifiers for polyvinyl chlorides.
U.S. Pat. No. 4,362,845 to Kamata et. al. relates to a composition with high impact resistance and little fish eyes content, comprising 97 to 60 parts by weight of a polyvinyl chloride-base resin and 3 to 40 parts by weight of a graft copolymer obtained by the three-stage graft polymerization of 65 to 25 parts by weight of a monomer combination (B) comprising 12 to 57 percent by weight of methyl methacrylate, 1 to 24 percent by weight of at least one of alkyl acrylates having a C.sub.1-18 -alkyl group, 80 to 40 percent by weight of styrene and 0 to 3 percent by weight of a polyfunctional crosslinking agent having one or more alkyl groups in the molecule onto 35 to 75 parts by weight of a butadiene-base elastomer (A) containing 30 percent by weight or more of 1,3-butadiene units.
Although the impact modified CPVC compounds described above are useful, the compounds contain carbon based impact modifiers and therefore provide more fuel to increase the rate of heat release and smoke generation when the compounds are burned. The addition of these types of impact modifiers to CPVC therefore produces less desirable properties in the compound than CPVC alone.
Therefore, a thermoplastic polymer compound comprising chlorinated polyvinyl chloride and an impact modifier having improved properties is desired. Preferably, the thermoplastic polymer compound will have increased stability, toughness and a low rate of heat release and smoke generation.